1. Field of the Invention
The present invention relates a laminated optical film which is used for a liquid-crystal display device and which has excellent reworkability after sticking of the laminated optical film onto a liquid-crystal cell, as well as excellent machining characteristic and excellent dimensional accuracy, and to provide a method for producing the laminated optical film and a liquid-crystal display device using the laminated optical film.
2. Description of the Related Art
Shock resistance of a liquid-crystal display element and space saving of a liquid-crystal display device have been requested with the advance of spread of cellular phones in recent years. To satisfy the two requests, it is necessary to connect a backlight unit to a liquid-crystal cell constituting a liquid-crystal display device. In order to achieve the space saving, not a mechanically connecting method but a fixing method using a double-sided adhesive tape or the like is used. The double-sided adhesive tape is stuck onto an optical film stuck onto the liquid-crystal cell because there is no place where the double-sided adhesive tape is stuck onto a liquid-crystal cell substrate in order to save the space.
FIG. 8 is a sectional view showing the configuration of a related-art liquid-crystal display device. Phase retarders 22 and 22xe2x80x2 and polarizers 21 and 21xe2x80x2 are laminated successively on opposite surfaces of glass substrates 23 and 23xe2x80x2 respectively. A luminance-enhancement film 26 is further laminated on the backlight-side polarizer 21. The luminance-enhancement film 26 is bonded to a backlight unit 34 through a double-sided adhesive tape 29. In the liquid-crystal display device provided with such a backlight, the luminance-enhancement film is used for enhancing luminance. A light polarizer-integrating type luminance-enhancement film constituted by a combination of a polarizer and a luminance-enhancement film stuck onto the polarizer is often used. A laminated optical film prepared by sticking a polarizer and a luminance-enhancement film of the same size to each other is generally used as the light polarizer-integrating type luminance-enhancement film.
The laminated optical film is processed into a size larger than the size of a display screen of the liquid-crystal display device. The optical film is stuck onto a liquid-crystal cell so that the displayable range of the liquid-crystal cell is covered with the optical film to prevent a phenomenon that a part of light entering the optical film from the backlight is missing in end portions of the film.
A problem, however, arises in a module reworking step if there is an adhesive layer weak in adhesive strength for sticking respective films or another layer weak in adhesive strength in the case where a double-sided adhesive tape is directly stuck onto a backlight-side optical film portion because a backlight unit is bonded to a liquid-crystal cell onto which an optical film is stuck as described above. That is, when a reworking operation is carried out to detach the backlight because a failure is found in the backlight after the backlight unit is bonded to the liquid-crystal cell, there is the possibility that the optical film may be broken. Also when intensive shock such as falling impact is given, the problem upon breaking of the optical film arises because force is concentrated into the laminated optical film which is a joint portion between the liquid-crystal cell and the backlight unit. Particularly, the luminance-enhancement film is weak in adhesive strength because the luminance-enhancement film is often provided as a laminate of a plurality of layers. Accordingly, the problem occurs easily in the luminance-enhancement film.
An object of the invention is to provide a laminated optical film which can solve the problem in the related art, which is used for a liquid-crystal display device and which has excellent reworkability after sticking of the laminated optical film onto a liquid-crystal cell, as well as excellent machining characteristic and excellent dimensional accuracy, and to provide a method for producing the laminated optical film and a liquid-crystal display device using the laminated optical film.
To achieve the foregoing object, in accordance with the invention, there is provided a method of producing a laminated optical film constituted by a laminate of a plurality of optical films different in area, the method including the steps of:
laminating an optical film (B) having a plurality of rectangular holes parallel to one another, on at least one surface of an optical film (A) to thereby form a laminate; and
cutting the laminate into a plurality of chips.
Preferably, in the producing method according to the invention, the optical film (A) is a polarizer whereas the optical film (B) is a luminance-enhancement film.
Preferably, in the producing method according to the invention, the optical film (A) is an optical film including at least one retardation film or viewing angle compensating film laminated on a surface opposite to a surface through which the optical film (A) is stuck onto the optical film (B).
Preferably, in the producing method according to the invention, the optical film (B) is an optical film constituted by a combination of cholesteric liquid crystal and a xcex/4 plate.
Preferably, in the producing method according to the invention, the optical film (A) and the optical film (B) are laminated on each other through a pressure sensitive adhesive.
According to the invention, there is provided a laminated optical film produced by the method, the laminated optical film having extruded portions formed from the optical film (A), the laminated optical film having at least one side surface cut in a plane.
According to the invention, there is provided a liquid-crystal display device including a liquid-crystal cell, and at least one laminated optical film defined above and disposed on at least one surface of the liquid-crystal cell.
Preferably, in the liquid-crystal display device according to the invention, at least one of the extruded portions of the laminated optical film is stuck onto a surface light source through a double-sided adhesive tape.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.